Razor blades and process for making same

ABSTRACT

THIS APPLICATION IS CONCENTRATED WITH PROCESSES FOR PRODUCING NOVEL STEEL WHICH, IN ITS FINISHED FORM, IS AT LEAST 80% AUSTENITIC AND IN PREFERRED EMBODIMENTS IS SUBSTANTIALLY FULLY AUSTENITIC, BUT YET HAS AT LEAST THE HARDNESS AND STRENGTH OF HIGH CARBON MARTENSITIC STEELS. THE HARDNESS OF THE STEEL PLUS ITS TEMPER-RESISTANCE (DUE TO THE FACT THAT IT IS AUSTENITIC) MAKES IT ESPECIALLY USEFUL FOR MAKING CUTTING EDGES, E.G. KNIVES AND ESPECIALLY RAZOR BLADES HAVING IMPROVED TEMPER-RESISTANCE. THE STEEL IS MADE BY (A) HEATING A STEEL COMPRISING FROM ABOUT 7 TO ABOUT 30% MANGANESE AND ABOUT 0.6 TO ABOUT 1.;% CARBON TO AT LEAST THE AUSTENIZING TEMPERATURE TO MAKE IT FULLY AUSTENITIC AND TO DISSOLVE SUFFICIENT CARBIDES SO AS TO DEPRESS THE &#34;MS&#34; TEMPERATURE SUFFICIENTLY BELOW ROOM TEMPERATURE THAT THE STEEL WILL REMAIN MAINLY IN THE AUSTENITIC FORM, E.G. AT LEAST 80% AUSTENITIC, WHEN IT IS BOTH COOLED, PREFERABLY BY QUENCHING, TO ROOM TEMPERATURE AND SUBSEQUENTLY COLD-WORKED; (B) COLD-WORKING THE STEEL AND (C) THEREAFTER AGE-HARDENING THE STEEL. IN A PREFERRED PROCESS FOR MAKING RAZOR BLADES FROM SUCH STEELS, THE CUTTING EDGE IS FORMED BETWEEN THE COLD-WORKING STEP AND THE AGEING STEP.

United States Patent 3,756,865 RAZOR BLADES AND PROCESS FOR MAKING SAME Aiyaswami Suryanarayan Sastri, Stow, Mass., assignor to The Gillette Company, Boston, Mass. No Drawing. Filed Nov. 1, 1971, Ser. No. 194,166 Int. Cl. C22c 39/30, 39/32; C21d 9/18 US. Cl. 148-12 16 Claims ABSTRACT OF THE DISCLOSURE This application is concerned with processes for producing novel steel which, in its finished form, is at least 80% austenitic and in preferred embodiments is substantially fully austenitic, but yet has at least the hardness and strength of high carbon martensitic steels. The hardness of the steel plus its temper-resistance (due to the fact that it is austenitic) makes it especially useful for making cutting edges, e.g. knives and especially razor blades having improved temper-resistance. The steel is made by (a) heating a steel comprising from about 7 to about 30% manganese and about 0.6 to about 1.4% carbon to at least the austenizing temperature to make it fully austenitic and to dissolve suflicient carbides so as to depress the Ms temperature sufliciently below room temperature that the steel will remain mainly in the austenitic form, e.g. at least 80% austenitic, when it is both cooled, preferably by quenching, to room temperature and subsequently cold-worked; (b) cold-working the steel and (c) thereafter age-hardening the steel. In a preferred process for making razor blades from such steels, the cutting edge is formed between the cold-working step and the ageing step.

SUMMARY OF THE INVENTION In recent years, the shaving properties of razor blades have been substantially enhanced by the application to the cutting edge of polymeric coatings such as the fluorocarbons disclosed in US. Patent No. 3,071,856 to Irwin W. Fischbein. In applying such fluorocarbon coatings and especially the higher molecular weight polymers and telomers to blade edges, it is necessary to sinter the coatings at elevated temperatures, e.g. 288 C. to 427 C. Such temperatures have a softening eifect on both carbon and stainless steels which adversely affect their shaving properties. The stainless steels, although softer, where better able to withstand the sintering temperatures than the carbon steels and most of the first commercial applications of such coatings were on the former. Despite the sotfening of the steels, the fluorocarbon coatings still provide a substantial improvement in shaving comfort and ease. As can be appreciated, the benefits of such coatings would be even more fully realized if they could be applied to blades which intially had at least the hardness of carbon steels and which had substantially better temper-resistance.

One object of the present invention is to provide processes for making novel steel, which in its finished form, is mainly austenitic, e.g. at least 80% (with the accompanying good temper-resistance) but which has hardnesse and strength which are at least comparable of those of high carbon martensitic steel.

Another object is to provide new and improved cutting edges such as knives and scalpels and especially razor blades comprising said steel.

Other objects should be obvious from the following description and claims.

In general, the above objects are achieved by (a) heating a steel comprising carbon and manganese in the ranges specified below to at least the austenizing temperature for a suflicient time to make it fully austenitic and to dissolve sufiicient carbides so as to depress the Ms temperature Patented Sept. 4, 1973 sufiiciently below room temperature that the steel will remain mainly in the austenitic form when it is both cooled to room temperature, preferably by quenching, and subsequently cold-Worked; (b) cold-working the steel and (c) thereafter age-hardening the steel. In a preferred mode of making razor blades, the cutting edge is formed, e.g. by grinding between the cold-working step and the age hardening step.

Generally, the blades of the present invention are made from steels which comprise by weight about 0.6 to about 1.4% carbon, about 7 to 30% manganese and the balance iron or iron and other alloying elements which will enhance the properties of the steel but not interfere with the processes. In preferred embodiments, the steels may contain one or more alloying elements which are known to decrease the stacking fault energy of the steel. As examples of such elements (and the range in which they may usually be present), mention may be made of the following:

Percent Chromium 0 to 16 Cobalt 0 to 10 Silicon 0 to 2 Aluminum 0 to 6 Copper 0 to 2 Percent Molybdenum 0 to 2 Nickel 0 to 5 Tungsten 0 to 1 In preferred embodiments, the steel will contain sufficient chromium so as to render it stainless. Usually this can be accomplished by incorporating at least 10% chromium into the composition. In the embodiments which will be the most commercially feasible, usually the steel will contain between about 10 to 20% chromium. When appreciable amounts of chromium are added such as set forth above to enhance the corrosion-resistance of the steel, larger amounts of manganese should be present in order to offset the carbide-forming propensity of the chromium. In steels containing, for example, 10 to 20% chromium, it will usually be advisable to have about 15 to 30% manganese present. In steels containing 10 to 16% chromium, it will be generally advisable to have about 15 to 25%. In steels which include less than 2% chromium, the manganese will preferably be present in amounts ranging between about 7 to 14%. As an example of a steel which has been found especially useful in the processes of this invention, mention may be made of one containing 1.0% carbon, 14% chromium, 21% manganese and the balance iron with the small amounts of impurities normally found therein. Another steel which was found useful in the processes of the invention contained 1.01% carbon, 12.3% manganese and the balance iron with the small amounts of impurities normally found therein.

In carrying out the processes of the present invention, the steel is heated to at least the austenizing temperature, for a sufiicient time, to make it fully austenitic and to dissolve sufficient carbides so as to depress the Ms temperature sufficiently below room temperature that the steel will remain mainly austenitic, e.g. at least when it is both cooled, preferably by quenching, and subsequently cold-worked. In preferred embodiments, the steel is so heat treated that the Ms" temperature will be at least below C. and preferably below 200 C. Generally, for most steels within the scope of this disclosure, the Ms temperature can'be sufficiently depressed by heating the steel to a temperature between about 1000 C. and 1250 C. and holding it there for periods from at least 1 minute to 1 hour; with the longer times being used for the lower temperatures. In preferred embodiments, the steel is heated to a temperature between 1050 C. and 1250 C. Particularly useful results were obtained by heating the steel to a temperature of 1050 C. and holding it there for about one half hour.

The cold-working step, which imparts a substantial increase in hardness to the steel, may be carried out by any of the well-known methods, e.g. rolling, stamping, pressing, drawing, etc. Further when the processes disclosed herein are used in making cutting edges such as razor blades at least a portion of the cold-working may be accomplished in the grinding operation which is used in forming the cutting edge. In preferred embodiments, the coldworking is carried out by cold-rolling. Generally the extent to which the steel can be cold-worked without being converted to martensite will depend upon the Ms temperature. Usually the lower the Ms temperature, the more the steel can be cold-worked without being appreciably converted to the martensitic form. It is generally desirable that the steel subsequent to cold-working contain less than 20% martensite and preferably less than In especially preferred embodiments, the steel is substantially fully austenitic subsequent to the cold-working step. Generally with a steel whose Ms temperature has been sufficiently depressed, e.g. to at least below 200 C. Substantial increases in the hardness can be achieved by coldworking the steel until there has been a reduction in thickness of at least 50%. Usually the maximum hardness which can be obtained in the cold-working step will generally be achieved by cold-working the steel until there has been a reduction in thickness of at least between about 70% and 96%. It is to be understood that reductions beyond this extent may be made, but generally they will not result in additional hardening.

In using the processes of the present invention for producing cutting edges such as razor blades, the cold-Working which is necessary to provide the maximum hardness which is obtainable in this step may be provided at least in part by the grinding step which is normally employed in forming the cutting edge. Thus, if desired, one may, for example, partially harden the strip by, for example, coldrolling; carry out any desired stamping or perforation steps and then complete the cold-working step at least in the edge area by the grinding operation. Of course, it will be understood that when desired, substantially all the cold-working may be carried out, for example, by coldrolling and the grinding step would contribute little additional hardening. In such event, if desired, electrosharpening methods could be employed in forming the cutting edge. In preferred modes of making razor blades, the edge is formed prior to the age-hardening step when the steel is not as hard. It should be understood, however, that, when desired, the cutting edge may be formed subsequent to the age-hardening step but the steel will be appreciably harder. Generally, the methods which may be employed for forming the cutting edge are well-known to the art and the specifics thereof form no part of this invention.

The age-hardening step, which is carried out subsequent to the cold-working step is a time, temperature dependent reaction in which a further substantial increase in hardness is achieved. Generally, the optimum hardnesses will be achieved by heating the steel at a temperature between about 200 C. and 500 C. for periods, for example, of at least from about ten seconds to ten days. As will be appreciated, the shorter times will be applicable to the higher temperatures and the longer times to the lower temperatures. Further with steels that are essentially iron, manganese and carbon alloys, the age-hardening step should be preferably carried out at temperatures below 425 C. In carrying out the age-hardening step, excessively high temperatures for extended periods should be avoided in order to prevent over-ageing. With the steel containing 1.01% carbon, 12.3% manganese and the balance iron, optimum hardness was achieved by heating it for about three and one-half hours at 350 C. With the steel containing 1% carbon, 14% chromium and 21% manganese, optimum hardness was achieved by heating it at 350 C. for three hours.

The following non-limiting examples illustrate the processes of the present invention as it relates to the preparation of a razor blade.

EXAMPLE 1 A strip of steel containing 1.00% carbon, 21% manganese, 14% chromium and the balance iron and the usual trace impurities found therein, was made fully austenitic by heating it at 1200 C. for one-half hour and thereafter cooling it rapidly in water. The strip which had a hardness of 220 DPHN was cold-rolled to a thickness of four thousandths of an inch with a reduction of 96% in the thickness of the steel. The hardness was 740 DPHN and the strip was still substantially fully austenitic. The strip was then sharpened to produce an edge through conventional razor blade sharpening techniques. Subsequent to sharpening, the blade was heated to 350 C. for three hours and the body hardness rose to 885 DPHN and was still substantially fully austenitic. A polytetrafiuoroethylene telomer coating was applied to the cutting edge and it was cured thereon at 343 C. for ten minutes. The following table illustrates the temper-resistance of the blades of the present invention during the polytetrafiuoroethylene sintering step as compared with typical carbon and stainless steel blades.

Body Slntering temperature Body A steel strip containing 1.01% carbon, 12.3% manganese and the balance iron and the usual trace impurities found therein, was made fully austenitic by heating it at 1050 C. for one-half hour and thereafter quenching it to room temperature in water. The strip which had a hardness of 200 DPHN was cold-rolled to a thickness of four thousandths of an inch with a reduction of in the thickness of the steel. The hardness was 750 DPHN and the strip was still substantially fully austenitic. The strip was then sharpened to produce an edge through conventional razor blade sharpening techniques. Subsequent to sharpening, the blade was heated to 350 C. for about three and one-half hours and the body hardness rose to 850 DPHN and was still substantially fully austenitic. A polytetrafiuoroethylene telomer coating was applied to the cutting edge and it was cured thereon at 343 C. for ten minutes. Subsequent to the cure, the blade had a body hardness of 850 DPHN which is substantially better than that of the typical carbon or stainless blades set forth in Example 1.

EXAMPLE 3 Blades were prepared by a process similar to that of Example 2 except that the age-hardening step was carried out at 400 C. for fifteen minutes. The results were comparable to those of Example 2.

It should be understood that when desired the agehardening and polymer sintering step can be carried out simultaneously.

The steels of this invention due to their austenitic nature are generally non-magnetic and also have good low-temperature ductility. Accordingly, in addition to being useful for making cutting edges such as razor blades, they are also useful for other purposes in which one or more of their useful properties is desired, e.g. springs, cryogenic hardware, high-strength wire and cable, and any other end uses where their good temper-resistance may be useful.

Having thus described my invention what is claimed is:

1. A process for making razor blades, the edges of which in their finished form are mainly austenitic, have hardnesses which are at least comparable to high carbon martensitic blade edges, and have improved temper-resistance, said process comprising (a) heating a steel strip which comprises from about 7 to 30% manganese and 0.6 to about 1.4% carbon to at least the austenizing temperature for a sufficient time to make it fully austenitic and to dissolve sufi'icient carbides so as to depress the Ms temperature of said steel sufficiently below room temperature that the steel will remain mainly in the austenitic form when it is both cooled to room temperature and subsequently cold-worked; (b) cold-working the steel strip at least in the areas in which the cutting edge is to be formed; (c) age-hardening the steel and (d) at some time subsequent to the austenizing step forming the cutting edge.

2. A process as defined in claim 1 wherein the steel is quenched to room temperature subsequent to the austenizing step.

3. A process as defined in claim 1 wherein said agehardening step is carried out at a temperature between about 200 C. to 500 C. for a period of at least about ten seconds to ten days.

4. A process as defined in claim 1 wherein said blade edge in its finished form is at least 80% austenitic and wherein in the initial heating step said steel is heated to a temperature between 1000" C. to 1250" C. for a period of at least one minute to one hour and wherein said ageing step is carried out at a tempeprature between about 200 C. to 500 C. for periods of at least from about ten seconds to ten days.

5. A process as defined in claim 1 wherein said steel is cold-worked until there has been a reduction in thickness of at least about 50%.

6. A process as defined in claim 1 in which said steel includes at least one alloying element which reduces the stacking fault energy of said steel.

7. A process as defined in claim 1 wherein said steel contains less than 2% chromium and between 7 to 14% manganese.

8. A process as defined in claim 1 wherein said steel includes 10 to 20% chromium and from 15 to 30% manganese.

9. A process as defined in claim 1 wherein said steel includes 10 to 16% chromium and from 15 to 25% manganese.

10. A process as defined in claim 1 wherein the cutting edge of said blade in its finished form is substantially fully austenitic.

11. A process as defined in claim 1 wherein at least a portion of cold-working in the cutting edge area is provided by the work involved in the forming of the cutting edge by grinding.

12. A steel razor blade having a cutting edge which is mainly austenitic and which comprises 0.6 to 1.4% carbon and 7 to 30% manganese.

13. A steel razor blade as defined in claim 12 which has stainless properties and includes about 10 to 20% chromium.

14. A steel razor blade as defined in claim 12 in which the cutting edge is substantially fully austenitic.

15. A steel blade as defined in claim 13 in which the cutting edge is substantially fully austenitic.

16. A razor blade, the cutting edge of which in its finished form, is mainly austenitic, has a hardness which is at least comparable to high carbon martensitic blades and which has improved temper-resistance, said blade being made from steel which comprises about 0.6 to 1.4% carbon and about 7 to 30% manganese.

References Cited UNITED STATES PATENTS 2,862,812 12/1958 Dulis et al. -126 B 3,116,180 12/1963 Malzacher 148--l2.4 3,281,287 10/1966 Edstrbm et al. 148-l2.4 3,425,877 2/ 1969 Deacon 148-12.4 3,575,737 4/1971 Carlen et al. 148-l2.4

WAYLAND W. STALLARD, Primary Examiner US. Cl. X.R. 

